Pseudo-satellite transmitter and method of transmitting GPS signals using pseudo-satellite transmitter

ABSTRACT

A method of transmitting GPS signals of a pseudo-satellite includes: enabling a GPS unit of a pseudo-satellite transmitter to generate a GPS signal; enabling a transmission power control unit to generate a plurality of GPS signals with different power levels based on the GPS signal and power determination values of a plurality of reception areas; and transmitting the GPS signals with different power levels to the plurality of reception areas through a plurality of different antennas.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of co-pending U.S.application Ser. No. 12/652,339 filed Jan. 5, 2010, which claimspriority to Korean Patent Application 10-2009-0001787, filed on Jan. 9,2009, in the Korean Intellectual Property Office, the disclosures ofwhich are each incorporated by reference herein in their entireties.

BACKGROUND

1. Technical Field

Exemplary embodiments of the present invention relate to apseudo-satellite transmitter and a method of transmitting GPS signalsusing a pseudo-satellite transmitter.

2. Discussion of Related Art

A global positioning system (GPS) is a navigation satellite system thatprovides reliable positioning, navigation, and timing services toworldwide users on a continuous basis. A receiver of a GPS systemcalculates its position by timing the signals sent by GPS satelliteshigh above the Earth. Each satellite continually transmits messageswhich may include the time the message was sent, orbital information,general system health, rough orbits of all GPS satellites, etc. The GPSreceiver utilizes the messages it receives to determine the transit timeof each message and computes the distances to each satellite.

GPS has been used by the U.S. Navy since the early 1970s and was openedto the public in 1984. By the early 2000s, the number of GPS users hadrapidly increased and the GPS had become part of vehicle navigationsystems and location-based services (LBS). LBS is an information andentertainment service, accessible with mobile devices through the mobilenetwork and utilizing the ability to make use of the geographicalposition of the mobile device. LBS can include mobile commerce whentaking the form of coupons or advertising directed at customers based ontheir current location, personalized weather services, location-basedgames etc.

However, GPS is limited to the environment in which the GPS receiver islocated. For example, obstructions and interferences in the environmentbetween the GPS receiver and the satellites may prevent the GPS receiverfrom receiving the signals it needs and at the quality level required toperform calculations. A GPS receiver typically needs to receive four ormore GPS satellite signals to determine the coordinates of athree-dimensional position. If one or more of these signals is notreceived, the GPS receiver may be able compensate for the missinginformation by utilizing other information that is present.

For example, a GPS receiver may make use of information provided from apseudo-satellite in a shadow area. The shadow area is an area wherethree or less signals are received or the quality of the received signalis poor due to a bad reception environment. A base station thattransmits GPS signals, such as GPS satellite signals, to the shadow areais called the pseudo-satellite.

The signals transmitted from the GPS satellites are based on a Codedivision multiple access (CDMA) system where an orthogonal code of eachsignal is used to discriminate a satellite ID. CDMA signals share afrequency and time. Therefore, when all the received signals do not havethe same power level, interference between a signal with a weak powerlevel and a signal with a strong power level occurs, which is called thenear-far problem.

Since all of the GPS satellites are disposed at similar heights (e.g.,about 25,000 Km from the ground), there is little variation in theintensity of the received signal. Therefore, the near-far problem doesnot arise. However, when the pseudo-satellite is used, the base stationis disposed at a height which is quite different from that of the actualGPS satellites (e.g., several tens of meters to several hundreds ofmeters). Therefore, there is a large variation in the intensity of thereceived signal from the pseudo-satellite as compared to the signalsfrom the actual GPS satellites.

Thus, there is a need for a GPS system that is capable of interfacingwith a pseudo-satellite that can improve GPS calculations using GPSsignals from GPS satellites and pseudo-satellites, and devices andmethods for implementing the GPS system.

SUMMARY

A pseudo-satellite transmitter according to an exemplary embodiment ofthe inventive concept includes a GPS unit, a transmission power controlunit, and a plurality of antennas. The GPS unit generates a GPS signalof a pseudo-satellite. The transmission power control unit generates aplurality of GPS signals having different power levels from the GPSsignal generated by the GPS unit and a distance from a shadow area tothe pseudo-satellite transmitter. Each of the antennas is configured towirelessly transmit the GPS signals with different power levels outputfrom the transmission power control unit to a corresponding one of aplurality of shadow areas according to the distance from the shadow areato the corresponding antenna. The pseudo-satellite transmitter mayfurther include a control unit generating a control signal in responseto an external signal, where the GPS unit transmits the GPS signal inresponse to a control signal.

The multiple antennas may be annular antennas having a laminatedstructure of a plurality of antennas. The annular antennas may include afirst antenna (e.g., a weak power antenna) wirelessly transmitting theGPS signal with a first power level (e.g., a weak power level), a secondantenna (e.g., a medium power antenna) wirelessly transmitting the GPSsignal with a second power level (e.g., a medium power level), and athird antenna (e.g., a strong power antenna) wirelessly transmitting theGPS signal with a third power level (e.g., a strong power level). Themultiple antennas may be directional antennas that locally transmit theGPS signals only to a GPS shadow area.

A method of sending GPS signals from a pseudo-satellite transmitteraccording to an exemplary embodiment of the inventive concept includesdividing, by the pseudo-satellite transmitter, a reception area of aplurality of antennas into a plurality of divided areas at apredetermined distance interval from a transmission position of theantennas, and transmitting, by the pseudo-satellite transmitter, a GPSsignal representative of the location of the pseudo-satellitetransmitter from each antenna such that an electric field intensity ofeach of the divided areas are equal or similar to each other.

The antennas may be co-located in a lateral direction over thetransmission position. The divided areas may be annular and arrangedconcentrically around the transmission position. The lateral directionmay be the vertical direction. The antennas may be directional antennasand the divided areas may be annular and non-overlapping.

A method of transmitting GPS signals of a pseudo-satellite according toan exemplary embodiment of the inventive concept includes enabling a GPSunit of a pseudo-satellite transmitter to generate a GPS signal,enabling a transmission power control unit of the pseudo-satellitetransmitter to generate a plurality of GPS signals with different powerlevels based on the GPS signal and power determination values of aplurality of reception areas, and transmitting the GPS signals withdifferent power levels to the plurality of reception areas through aplurality of different antennas.

The transmitting may include transmitting a GPS signal of the pluralityhaving the lowest power level to the reception area of lowest area, andtransmitting each subsequent GPS signal of a next higher power level tothe next reception area of the next higher area. Alternately, when theantennas are directional antennas, the transmitting may includetransmitting all the GPS signals by each antenna to a respective one ofthe reception areas that do not overlap with one another.

BRIEF DESCRIPTION OF THE DRAWINGS

The inventive concept will become more apparent by describing in detailexemplary embodiments thereof with reference to the attached drawings inwhich:

FIG. 1 is a block diagram schematically illustrating a pseudo-satellitetransmitter according to an exemplary embodiment of the inventiveconcept;

FIG. 2 is a diagram illustrating the operation of multiple antennasaccording to an exemplary embodiment of the inventive concept;

FIG. 3 is a diagram illustrating the operation of multiple antennasaccording to an exemplary embodiment of the inventive concept; and

FIG. 4 is a flowchart illustrating a method of transmitting GPS signalsusing the pseudo-satellite transmitter according to an exemplaryembodiment of the inventive concept.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiments of the inventive concept will now be describedmore fully with reference to the accompanying drawings. Inventions basedon the inventive concept may, however, be embodied in many differentforms and should not be construed as limited to the exemplaryembodiments set forth herein. Like numbers refer to like elementsthroughout the description of the figures.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. Hereinafter, a pseudo-satellite transmitter and a method oftransmitting GPS signals using a pseudo-satellite transmitter accordingto exemplary embodiments of the inventive concept will be described indetail with reference to the accompanying drawings.

FIG. 1 is a block diagram schematically illustrating a pseudo-satellitetransmitter according to an exemplary embodiment of the inventiveconcept. As shown in FIG. 1, the pseudo-satellite transmitter includesmultiple antennas 50 that wirelessly transmit GPS signals with differentpower levels and a transmission power control unit 40 that generates theGPS signals with the different power levels according to a distance orposition of a GPS shadow area relative to the pseudo-satellitetransmitter or an antenna thereof and outputs them to the multipleantennas 50.

The transmission power control unit 40 may generate the GPS signals withthe different power levels in response to a control signal from acontrol unit 10, which may be controlled in response to an externalinput signal, a central processing unit, etc. The control unit 10 mayoutput a control signal to a GPS unit 20 and control the transmissionpower control unit 40 to generate GPS signals with multiple powerlevels. The GPS unit 20 may output one or more GPS signals includingpositional information (e.g., latitude and longitude) and temporalinformation (e.g., a time that the positional information is sent) ofthe pseudo-satellite at a predetermined time interval according to auniversal communication protocol. For example, the GPS unit 20 mayoutput information at a transmission rate of about 50 bps or more. TheGPS unit 20 may include a high-precision clock (not shown), such as anatomic clock or a quartz clock, which may be used to notify a GPSreceiver (not shown) of the current time. The pseudo-satellitetransmitter or a particular element of the transmitter such as the GPSunit 20 may further include a memory (not shown) that stores powerdetermination values from the multiple antennas 50 to reception areas.

The GPS receiver can detect the position, the movement distance, and themoving speed of an object from information output from the GPS unit 20using at least one of a trigonometrically function, a polar coordinatesystem, and a spherical coordinate system. The GPS receiver maycalculate a time difference during movement and divide a movementdistance by the time difference to calculate a moving speed of theobject. The GPS receiver can detect these data from GPS signals outputby actual GPS satellites and from the information output from thepseudo-satellite.

The positional information and temporal information output from the GPSunit 20 may be modulated or encoded for wireless transmission. A signalprocessing unit 30 including an analog signal converter 32 may signalprocess the positional information and temporal information. The signalprocessing may include an operation of processing (e.g., encoding) thepositional information and temporal information into acoarse/acquisition code (C/A) or a standard code, which is a civilcommunication navigation message, or a precision code (P code) formilitary purposes. The P code is combined with other unpublished codesand is then encoded. An algorithm for encoding the combination of the Pcode and the unpublished codes may be provided in the signal processingunit 30. The C/A code and the P code may be output at a bit rate of1.023 Mbps and a bit rate of 10.23 Mbps, respectively. Theabove-mentioned information may be carried on a carrier wave and thecarrier wave with the information may be modulated by the signalprocessing unit 30. In addition, the signal output from the analogsignal converter 32 may be amplified by an amplifier 34 and theamplified signal may be output to the transmission power control unit40.

Therefore, the transmission power control unit 40 may supply GPS signalswith different power levels to the multiple antennas 50. The receptionsensitivity of a signal received by a GPS receiver is reduced as thedistance of the GPS receiver from the multiple antennas 50 is increased.This is because the signal is radially transmitted from the multipleantennas 50 in all directions or it is attenuated while propagatingthrough the air. The attenuation of the signal may be proportional tothe reciprocal of an exponential function of the distance. Power that isproportional to the exponential function may be supplied to the multipleantennas 50 considering the loss of power during the propagation ofsignals. In this way, reception sensitivity may be obtained that doesnot depend on the position of the GPS receiver. Therefore, in anexemplary embodiment of the inventive concept, the transmission powercontrol unit 40 may output a signal whose power is proportional to anexponential function having a reception distance as a variable.

The multiple antennas 50 may be designed such that transmission signalsare received by a GPS receiver with the same or similar electric fieldintensity regardless of the reception distance, which will be describedbelow.

FIG. 2 is a diagram illustrating an operation of the multiple antennas50 according to an exemplary embodiment of the inventive concept.Referring to FIG. 2, the multiple antennas 50 transmit GPS signals whosepower is gradually increased to a plurality of annular reception areas(that is, GPS shadow areas) that are annular and are arrangedconcentrically around the position where the pseudo-satellitetransmitter is provided. For example, the annual area with the smallestarea (e.g., 11) receives a GPS signal of a lowest power level, theannual area of the next higher area (e.g., 22) receives a GPS signal ofa next higher power level, and the annual area of the highest area(e.g., 33) receives a GPS signal of the highest power level.

The multiple antennas 50 may include an annular antenna, a patternantenna, a patch antenna, an annular slot antenna having a laminatedstructure of several antennas, etc. The structure of the annular slotantenna may be embodied as that shown in U.S. Pat. No. 4,547,779, inwhich a microstrip annular antenna structure is formed by fourquarter-wavelength microstrip radiator patches arranged in a quadrantformation and having outwardly directed adjacent radiating apertureswhich together provide a composite annular radiating slot extendingabout 360° of azimuth.

The multiple antennas 50 may transmit the GPS signals to a large areawhile rising upward and transmit GPS signals with a higher power levelas a transmission distance between the reception areas and the antennas50 is increased. For example, the upper antenna (e.g., 56) may transmitthe GPS signal of the highest power level, the lower antenna (e.g., 54)may transmit the GPS signal of a lowest power level, and the middleantenna (e.g., 52) may transmit the GPS signal of a power level betweenthe lowest and highest power levels. Alternately, a lower antenna ratherthan an upper antenna may transmit a wideband GPS signal with a highpower level regardless of the height thereof.

Assuming that a reception area is divided into a weak reception area 11,a medium reception area 22, and a strong reception area 33, the multipleantennas 50 according to an exemplary embodiment of the inventiveconcept may include a weak power antenna 52 that wirelessly transmits aGPS signal with a weak power level, a medium power antenna 54 thatwirelessly transmits a GPS signal with a medium power level, and astrong power antenna 56 that wirelessly transmits a GPS signal with astrong power level. In FIG. 2, three antennas are shown and thereception area is shown as being divided into a corresponding threeareas. However, this is merely an example, as the reception area may bedivided into four or more areas. For example, when the reception area isdivided into n areas, n annular antennas may be provided. Thepseudo-satellite transmitter may transmit reception signals with a powerranging from about −120 dBm to about −130 dBm in the overall receptionarea.

Therefore, the multiple antennas 50 according to the embodiment of theinventive concept shown in FIG. 2 may transmit GPS signals with auniform intensity to a wide shadow area, which may be difficult forsatellite signals output from a space-based satellite 60 to reach.

FIG. 3 is a diagram illustrating the operation of multiple antennas 50according to an exemplary embodiment of the inventive concept. Themultiple antennas 50 are directional antennas (e.g., 58). Referring toFIG. 3, directional antenna 58 of the multiple antennas 50 according toan embodiment of the inventive concept transmits GPS signals withdifferent power levels to a GPS shadow area 74. GPS signals from aspace-based satellite 60 are receivable in the local GPS shadow area 74,while GPS signals from the other space-based satellites 70 may not bereceivable in the local GPS shadow area 74.

In an environment, such as a city, the GPS shadow area 74 appears in aportion of a GPS receivable area 72. When a pseudo-satellite GPS signalis transmitted only to the GPS shadow area 74, the GPS shadow area 74can use the pseudo-satellite GPS signal, and thus it may be possible toprevent interference between the signals transmitted from thepseudo-satellite transmitter to the GPS shadow area and signalstransmitted from the space-based satellite 60 to the GPS receivable area72.

The other directional antennas illustrated in FIG. 3 of the multipleantennas 50 (e.g., see other diamonds) function in a similar manner tothe above described directional antenna 58. For example, each otherdirectional antenna transmits GPS signals of different power levels tocorresponding local shadow areas as shown in FIG. 3. Therefore, themultiple antennas 50 according to an exemplary embodiment of theinventive concept shown in FIG. 3 may enable a GPS receiver to receiveGPS signals with the same or similar reception power in a local GPSshadow area where satellite signals from a space-based satellite 60cannot reach.

Therefore, the pseudo-satellite transmitter according to embodiments ofthe inventive concept may use the multiple antennas 50 according to FIG.2 or FIG. 3 to enable a GPS receiver to receive GPS signals with thesame or similar power in near and far reception areas or a local GPSshadow area.

A method of transmitting GPS signals using a pseudo-satellitetransmitter having the above-mentioned structure according to anexemplary embodiment of the inventive concept will be described below.In a method of transmitting GPS signals using a pseudo-satellitetransmitter according to an exemplary embodiment of the inventiveconcept, an area in which the multiple antennas 50 transmit signals isdivided into a plurality of reception areas at a predetermined distanceinterval from the transmission position of the multiple antennas. Theelectric field intensities of the signals transmitted to the receptionareas are controlled to be equal or similar to each other. In this way,the interference between the GPS signals may be reduced. In addition,transmitting GPS signals only to the GPS shadow area may reduce signalinterference in a GPS receivable area.

FIG. 4 is a flowchart illustrating a method of transmitting GPS signalsusing a pseudo-satellite transmitter according to an exemplaryembodiment of the inventive concept. As shown in FIG. 4, in the methodof transmitting GPS signals using the pseudo-satellite transmitteraccording to an exemplary embodiment of the inventive concept, thecontrol unit 10 and the GPS unit 20 of the pseudo-satellite transmitterare initialized if necessary (S10). For example, step S10 may be skippedif the control unit 10 and the GPS unit 20 were previously initialized.

After the control unit 10 and the GPS unit 20 of the pseudo-satellitetransmitter are initialized, the GPS unit 20 generates one or more GPSsignals and power determination values for the reception areas stored ina memory are read (S20). The GPS unit 20 may generate the GPS signals inresponse to a control signal from control unit 10. The GPS unit 20 mayread the values from its' own memory or a memory of the pseudo-satellitetransmitter. The GPS unit 20 may send these values to the transmissionpower control unit 40. Alternately the transmission power control unit40 may read the values from the memory.

The transmission power control unit 40 generates GPS signals withdifferent power levels for the reception areas based on one or more GPSsignals generated by the GPS unit 20 and the power determination values(S30). The number of reception areas may be n (e.g., a positive integer)and a GPS signal having an optimal power level (e.g., ranging between aweak level to a strong level) may be applied to each of the receptionareas according to a distance between pseudo-satellite transmitter or anantenna thereof and a corresponding reception area.

The GPS signals with different power levels for the reception areas,which are generated in Step S30, are transmitted to each reception areathrough the multiple antennas 50 (S40). A GPS receiver in each receptionarea may receive GPS signals with the same or similar power leveltransmitted through the multiple antennas 50.

While exemplary embodiments of the inventive concept have been shown anddescribed with reference to FIGS. 1 to 4, it will be understood by oneof ordinary skill in the art that various changes in form and detailsmay be made therein without departing from the spirit and scope of thedisclosure.

What is claimed is:
 1. A method of transmitting GPS signals of apseudo-satellite, comprising: enabling a GPS unit of a pseudo-satellitetransmitter to generate a GPS signal; enabling a transmission powercontrol unit to generate a plurality of GPS signals with different powerlevels based on the GPS signal and power determination values of aplurality of reception areas; and transmitting the GPS signals withdifferent power levels to the plurality of reception areas through aplurality of different antennas.
 2. The method of claim 1, whereinplurality of antennas are co-located in a lateral direction over acommon transmission position and the reception areas are annular andarranged concentrically around the common transmission position.
 3. Themethod of claim 2, wherein the antennas are co-located in a lateraldirection over the transmission position.
 4. The method of claim 2,wherein the transmitting comprises transmitting a GPS signal of theplurality of GPS signals having the lowest power level to the receptionarea of lowest area, and transmitting each subsequent GPS signal of anext higher power level to the next reception area of the next higherarea.
 5. The method of claim 4, wherein the transmitting comprisestransmitting all of the GPS signals by each directional antenna to arespective one of the reception areas.
 6. The method of claim 1, whereinthe antennas are directional antennas and the reception areas areannular and do not overlap with one another.